HyperLink hlRow = new HyperLink();
hlRow.Style.Add("color", "#000000");
hlRow.Style.Add("text-decoration", "none");

a.abc:hover {
    ...
}

LiteralControl ltr = new LiteralControl();
        ltr.Text = "<style type="text/css" rel="stylesheet">" +
                    @".d
                    {
                        background-color:Red;
                    }
                    .d:hover
                    {
                        background-color:Yellow;
                    }
                    </style>
                    ";
        this.Page.Header.Controls.Add(ltr);
        this.HyperLink1.CssClass = "d";

HyperLink hlRow = new HyperLink();
hlRow.Attributes.Add("Style", "color:#000000");

<asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl="#">HyperLink</asp:HyperLink>

using System.Drawing;
using System.Web.UI;
using System.Web.UI.WebControls;

protected void Page_Load(object sender, EventArgs e)
{
    Style style = new Style();
    style.ForeColor = Color.Green;
    this.Page.Header.StyleSheet.CreateStyleRule(style, this, "#" + HyperLink1.ClientID + ":hover");
}

.disabled {
    color: grey;
    text-decoration: none !important;
}

LinkButton button = item.FindControl("lnkFileDownload") as LinkButton;
button.Enabled = false;
button.CssClass = "disabled";

a.foo { color : orange; }
a.foo:hover { font-weight : bold; }

lblMsg.Text = @"Your search result for <b style=""color:green;"">" + txtCode.Text.Trim() + "</b> ";